In a car external panel manufacturing process as is disclosed in for example Tokkai Sho 63-165072, published by the Japanese Patent Office in 1988, blank materials having different specifications are aligned, welded by a laser beam, and formed into a predetermined shape by a press. This process is widely used.
In this case, when there is a gap due to an error in the processing of the blank materials when one blank is aligned with another blank, laser welding does not proceed well and welding quality falls. When there is a gap of more than 0.1 mm in particular, welding defects are easily produced.
Also, when the plurality of edges of the blank materials are aligned to be welded and there is a dimensional error in the welding part of one of the edges, its effect may extend to the welding part of the other edges.